Stereoscopic modeling machine



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,u Nkm u Patented Oct. 16, 1945 UNITED STATES PATENT OFFICE STEREOSCOPIC MODELING MACHINE Louis A. Scholz, Dayton, Ohio Application August 11, 1944, Serial No. 549,106 7 Claims. (Cl. Sil-13.8)

(Granted'under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) -used to record variations of intensity of light from corresponding points on two stereoscopic photographs, and a cutting toolis moved over a plastic or other surface to be carved, to reproduce automatically a replica or counterpart in three dimensions of the photographed object. As the apparatus is wholly automatic, it imposes no eyestrain upon the attendant or operator', and does not require a high degree of skill. 'Ihe personal equation is completely eliminated, once the apparatus has been adjusted to the stereo pair it is to reproduce 'Ihe invention may be useful in relief map making, in sign-making, or in the ne arts, or wherever reproductions in relief or in intaglio are desired. As the invention depends on photoelectric cells (or their equivalent) which are so sensitive that they will pick up a dot as small as the circle of confusion ofthe most accurate lens, the apparatus may be many times more sensitive and accurate than the human eye. Other objects. and advantages will be apparent from the following description.

'Ihe prior art contains several references to apparatus for reproducing portraits, etc., in relief from stereoscopic photographs. The 'earliest known Patent No. 1,090,493 to Von Orel dated March 17, 1914, discloses a .carving tool guided by the hands of the operator While he looks through a monocular or binocular microscope at a pair of stereoscopic photographs. According to the Townsend Patent No. 1,486,814 dated March 1l, 1924, a grooving tool is moved horizontally and vertically over material to be out in relief or in intaglio, to reproduce in three dimensions the object of a pair of stereo photographs. Movement is effected by manual turning of three lead screws each controlling travel of the tool in one of three planes. By employing a pair of index ngers or pointers, the variations between the two stereo photographs may be measured, and the variation or displacement between any two like points on the stereos caused the cutting tool to cut vertically more or less deeply, proportionately to said displacement. James Dorn in Patent No. 2,047,013, dated July 7, 1936, shows schematically an arrangement for reproducing objects by passing light through the walls of a three dimensional model onto a light-sensitive device, the model being given synchronous axial and rotional movements so that the light is transmitted through every part of its walls. The light-sensitive device is hooked up with a cutting tool and the work is moved synchronously with the model and is shaped by the cutting tool to the same form as the model. The action depends on the transmission of light through varying thicknesses of the walls of the model and no stereoscopic photographs are employed. ,In Patent No. 2,283,226 dated May 19, 1942, H. B. Porter discloses a method and means for contouring aerial maps by scanning automatically stereoscopic photographs, but reproduction of the image or stereo pair is not contemplated. My invention has important advantages over all these disclosures,

since it provides for the first time a purely auto-A matic and highly sensitive and accurate machine for carving a three-dimensional image, in relief or in intaglio and on any desired scale, of an object photographed stereoscopically.

In the accompanying drawings showing diagrammatically the preferred form of apparatus for practicing the invention:

Fig. 1 is a plan View, omitting the electric wiring and other control details;

Fig. 2 is a side elevation partly in section;

Fig. 3 is a schematic wiring diagram;

Fig. 4 is a diagram in section, on a large scale, of a single photocell unit adapted for transmiss1on;

Fig. 5 is an elevation of the three cell unit;

Fig. 6' is a perspective schematic view of the control of vertical movement ofthe cutting tool; v

. the horizontal scale. Figs. 9 and 10 show light intensity graphs GI and G2 respectively, obtained by photometric methods, the area of Fig. 8 being comprehended within each graph, which is shown with profile P. The ordinates represent light intensities of the points of the earths surface along profile P, as viewed from the two camera positions indicated by the legends and arrows. It will be understood that due to the limitations of the drawing sheet, the actual elevation of the camera relative to the ground is not shown in Figs. 9 and l0. These intensity graphs are supercially identical, but when superimposed, as in Fig. 11, differences are readily apparent. I'hese differences are due to the foreshortening effect of the change of the camera position from position 1 to position 2, corresponding points of equal photographic density or intensity being given a horizontal displacement proportional'to D1, Dz, D3, etc. As shown, the graphs GI, G2 coincide as far as line A-A', indicating that there is no change in elevation in that portion of prole P, or Di equals zero. From line A-A' to line B-B, the original prole descends; thus the. intensity graph GI leads the intensity graph G2 until these graphs arr apart a distance equal to D2. From line B-B to line C-C the original profile ascends, and the intensity graph GI lags behind graph G2 until these graphs are spaced apart in the opposite direction a distance equal to D3. From C-C to line D-D, prole P descends, and again graph GI leads graph G2 until the graphs are coincident, at line D-D', showing that the original prole has returned to the starting level or datum plane. Now an automatic stereoscopic modeling machine need only compare the densities of the same point photographed on two stereo negatives (or positives) and then need only record the horizontal displacement of the two images of said point as vertical or altitude dilerences, on some material capable of taking and preserving the impressions in permanent form. This result is accomplished by the apparatus described herein.

The preferred apparatus is adapted to be supported on a ilat table top T (Fig. 2) on which a pair of steroscopic photographs I2, I2a of the same object are laid fiat'. Some arrangement may be made for supporting the photographs so that their relative positions may be slightly altered, as for instance by means of a pair of nethreaded manually operated screws acting on a frame holding one of the photographs and adapted lto move the framev parallel to the table top in either of two directions 'at right angles (not shown). tives, and a source or sources of light, preferably two electric lamps I3 (white or colored as desired) are located beneath the table, one lamp being below each negative, with a switch to control both lamps, as will be understood without illustration. Thus light rays pass through both negatives and Preferably the photographs are negamay be picked up at any point above either negative to activate light-sensitive cells to be described. The proper adjustment/of the relative position of the negatives may therefore be determined'optically by inspection of the negative against a horizontal grid (not shown) held above the table top prior topperating the apparatus.

Secured to the table top are four parallel guiding blocks I4, I5, I6, I1, each having a straight T-shaped slide or slot I8 cut in its upper face. An elongated flat guide rest I9 has its underside provided with tongues I9a to t in the slots I8; thus the guide rest I9 is spaced above the table top and may reciprocate parallel thereto directly above the photographs. For convenience, the direction of this reciprocation is herein termed lateral, while the direction at right angles thereto isV termed longitudinal Slidably mounted on top of the guide rest I9 is a tool support 20 having an arm 20a extending at right angles, a straight V-shaped slide 2I being provided on the upper surface of guide rest I9 for guiding relative sliding of the tool support. A vertical rotary cutting tool 22, driven and controlled as will be described later on, is carried by arm 20a and extends down into contact with or proximity to a reproductive bed 23 which may be of many different materials such as wood, plaster of Paris, wax compound, chalk, graphite or talc compound, a plastic, or other readily carved material having the necessary texture or reproductive sensitivity to reproduce small surfaces and lines. The bed 23 is shown as supported on the table top, 'and as it is to be carved, it must be clamped thereon (not shown). The outer end of arm 20a may be slidably supported on a guiding block 24 having a V-shaped groove 25 parallel to slide 2l, Another pair of parallel guiding blocks 26 are shown, each being fixed to the table top and having a V-shaped groove 21 parallel to slides I8, said guiding blocks 26 supporting and guiding block 24 when tool support 20 is moved laterally by sliding of guide rest I9 over slides I4-I1. The under side of block 24 will have V-shaped projections fitting in grooves 21, as will be understood. By the described arrangement, the cutting tool 22 is movable over the reproductive bed in either of two directions at right angles to each other, in a plane parallel to the table top. As the reproductive bed has its upper surface initially plane and parallel to the table top, such surface will be inscribed or carved when the cutting tool is properly actuated in vertical planes.

To move the tool support 20 along the guide rest I9, a small 3-terminal constant speed revers ing motor 30 is employed, and for convenience it is mounted on the guide rest, preferably on flange 3| which projects at right angles from one end of the guide rest. Motor 30 preferably is of the type which houses in its casing a solenoid braking clutch 32 (Fig'. 3)to cause it to stop quickly when de-energized, and preferably'has a reduction gear train (not shownl'also built vinside the casing. Similarvmotors are used to control various devices in aircraft, hence the motor is not described in detail. The gear train directly drives a lead screw 33 whose thread may be very fine; that is, having'a pitch of one one-hundredth of an inch, more or less. Similar lead screws are in use in sound recording and reproducing machines. Meshing with the threads of lead screw 33 is a nut 34 fixed to tool support 20. vThus nut 34 is moved back and forth to cause reciprocation of thel tool support. Reversal of motor 30 is obtained through limit switches 35, 36, which may be directly contacted by the traveling nut as it reaches leither limit of movement. The speed of motor 30 and the reduction through the described, gearing may cause the traveling nut to move from one extreme position to the other during one to five minutes, more or less, depending on the size of the stereoscopic photographs on the table and on the size of the reproductive bed, which it should be clear, may be many times larger than the photographs, although for convenience of illustration being shown as of the same size.

Movement along slides I4, I5, I6, I1 and 26 is controlled by a motor 31, driving a line-threaded vlead screw 38 (similar to lead screw 33) which is supported on bearings (not shown) fixed to the table top. Screw 38 engages a threaded boss 40a (Fig. 2) on the guide rest I9. Motor 31 is operated through relays 4l, 42 (Fig. 3) each time the traveling nut 34 contacts one of the limit switches 35, 36, thereby to move the entire assembly supported on slides I4--I1 through a small increment, which may be one two-hundredth of an inch. Thus the cutting tool 22 is moved along the entire length of the reproductive bed, then is advanced laterally through the desired increment and moved in the opposite direction along a Path parallel to the path rst traversed, then is advanced laterally through the same increment and moved along a third path parallel to the other two, and so on until the machine is stopped by the operator, or automatically if preferred. The cutting tool may be similar to a dental type drill'. and necessarily is of small diameter.

To drive the cutting tool continuously while the apparatus is operating, a motor 43 of perhaps one one-hundredth horsepower is employed and is supported on arm 20a by means not shown, with the cutting tool directed downwardly. If desired, a small fan (not shown) also driven by motor 43 may blow the line particles or grains dislodged by the cutting tool, so that there is no tendency for these loose particles to collect in depressions cut in the reproductive bed, which might cause some uncontrolled abrasion of the three-dimenr sional image being formed, with resultant distortion or blurring some of the surfaces of said image. Furthermore, a fan is desirable to prevent particles of a dust-like nature from settling on the negatives during operation of the machine. For this purpose an additional fan adjacent the negatives may be employed, 'or one large fan may be located directly over the apparatus to continually blow away all atmospheric dust as well as particles rising from the carving operation. Either arrangement will be understood without illustration. Instead of a fan or fans, a suction head (connecting with a vacuum line) may be located adjacent the cutting tool (not shown) to pick up particles from the surface of the reproductive bed during the carving.

The operation of any stereoscopic device depends on the foreshortening of any object proportionally to its height above the datum or base plane, which foreshortening takes place along the axis of separation; that is, the axis or straight line between common points of the stereo pair. The present, machine is so designed that it picks up density values of two correspondingpoints of the stereo pair, and compares these values and records (on the reproductive bed) a vertical cut equal to or proportionate to the horizontal displacement along said axis.

Toopick up and compare the density values of corresponding points of the stereo pair, I employ a unique arrangement of photocells and cooperating parts with one photocell unit 45 preferably xed to the tool support 20 tok participate in the longitudinal and lateral movements thereof (relative to photograph I2). To permit photocell unit 45 to be exposed to the light densities of every point of photograph i2, the guide rest is slotted, as best shown at 46, Fig. 2, so that no part of the guide rest is interposed between the photograph to be scanned and the scanning element 45. Obviously if the stereo photographs are located above the machine, as is entirely feasible, it is unnecessary to provide a slot 46, but the scanning element must then be reversed to pick up light densities fromthe photograph. Cooperating with unit 45 is a 3-cell analyzer unit 41 comprising photocells 48, 49, 50, which must be so located on the tool rest as to pick up light densities of three adjacent points of photograph I2a along a line parallel to the path of movement of the toolsupport on guide rest I9. Before explaining how three adjacent points of photograph I2a are picked up by the 3-cel1 unit, the interaction of the two units `should be outlined.

Let us suppose that photocell unit 45 is at the lower right hand corner of photograph I2, which may be considered as the starting point of the scanning operation, then the 3-ce1l analyzer unit 41 is moved by a vscrew 5I until the middle cell 49 is receiving light from the corresponding point on photograph I2a. Then operation is started by closing a, main switch 52 (Fig. 3) energizing motor 30 to cause travel of the tool rest to the left (as viewed in Fig. l) If while this travel occurs the intensity of a pin point of light reaching photocell unit 45 exactly equals the intensity of light striking photocell 49, there is an electrical balance.

. in a circuit including relay 53, which opens to deenergize motor 54, which may be a Selsyn unit, that is, a self-synchronous unit so built that when it is coupled electrically to a similar unit, it will duplicate any turningmov'ement thereof. It is not essential that a Selsyn unit be used as other reversible and quicklyv stopped motors could be employed. This action will be understood by studying Fig. 3. However, should the prole of the photographed object be rising or falling, the light intensities reaching photocells 45 and 49 will be unequal. If the profile is rising, photocells 45 and 5I] balance each other while photocells 48 and 49 do not. This condition energizes relays 53' and and leaves relay 56 de-energized, thus starting motor 54 to drive the 3-cell unit 41 to the right as viewed in Fig. l, until the middle photocell 49 is in the balancing position, when the circuit of motor 54 is opened. On the other hand, should the profile be falling, cells 45' and 49 will be unbalanced and 45 and 5l] will also be unbalanced, while cells 45 and 48 will be balanced, thus leaving relay 55 de-energized and relays 53 and 56 energized, which will start 'motor 54 to move the 3-cell unit to the left. Cell 49 always tends to be centered over the density point of photograph I2a that exactly equals the corresponding point of photograph i2. It will be clear that the 3-cell unit 41 analyzes automatically the direction in which the cutting tool should be moved to cut a profile like that of the object photographed. The 3-cell unit may therefore be considered as the brain of the machine, while the cutting tool is like a. hand directed by the brain Now referring to Fig. 4, which is a diagram of photocell unit 45, a photocell is mounted in one end of a sealed casing 6I which excludes all light from the cathode except the rays admitted through an achromatic lens system, here shown as a convex lens 62 andconcave lens 63. The lens system is housed in casing 6I, which tapers to a point where there is a tiny light aperture 64. This aperture is above the negative I2 through which light passes, from a light source shown as an electric lamp 65 carried in a. housing 66 having a reflector 61 and a converging lens 68 to focus the light rays to a point at the aperture 69 of the tapered end 1u of housing 66. With this arrangement, housing 66 must be supported on the underside of the negative I2 and must travel synchronously with the photocell unit 45 and to the same extent. There are various mechanical methods of accomplishing this result, none of which is shown.

In Fig. 5 there'is shown an arrangement for picking up light from three adjacent points in straight line succession and then transmitting the similar to aperture 64), about .02" in diameter and so located that it is directly above the light source. Light passing through negative |2a reaches the pointed tips of housings 1|, 12, 13 and is transmitted by said apertures to the lenses (each of which may be replaced by a lens system as in Fig. 4) and through the lenses to the sensitive cells 49, 49, 50.

A diagrammatic illustration of means for translating the variation or displacement between any two like points on the-stereo pair into vertical movements of the cutting tool is shown in Fig. 6. Here the three-cell unit 41 is shown as secured to a slide 80 supported'on tool support 20 and guided-by parallel angles or other guides 8|.

An elongated slot 62 in the tool support permits light rays to reach the three-cell unit 41. An arm 93 is fixed to slide 90 and has a threaded opening for receivingl a worm 90 which is on the end of shaft 9| driven by Selsyn type motor 54 also carried on the tool support. If desired, the worm 90 may be driven through reduction gearing (not shown) and it may have very line teeth to give close control of the position of three-cell unit 41, while the Seisyn" motor 54 may have several windings to permit increments of movement of as little as one-third of a revolution or less. A pulley 92 (or a sprocket wheel) ls fixed to shaft 9| and a belt 93 `(or a sprocket chain) is trained about part 92 and alsov about a pulley or sprocket 94 on a shaft 95 supported von motor head 96 on which the carving motor 43 is mounted. Guides are indicated to permit the motor head and motor to move vertically or at right angles to the top (outer surface) of the reproductive bed 23. A vertical rack 99 on the motor head is reciprocated by a pinion 99 xed to shaft 95. It will be clear that each time Selsyn motor 54 is energized, the three-cell unit 41 will be moved in one direction or the other, the total movement permitted being, however, not over 15% of the length of the photographs |2, |2a. Simultaneously, the motor head and the rotating cutting tool 22 will be moved up or down. Obviously, the reduction gear between motor 54 and shaft 9| and slide 60 may have almost any ratio and hence, the vertical movement of the cutting tool may be magnified or decreased in accordance with the desired results on the reproductive bed.

Now referring to Fig. 3, a source of electricity l| is connected through main switch 52 with leads I0 to which the cutting motor 43 is coupled in series by conductors |02, |03. The longitudinal scanning motor 30 is joined by conductors |04 and |02 to one of the leads |0| and is coupled through conductors |05, |06.to motor 31, which eii'ects lateral motion of the tool rest 20 during scanning, as described above. A double pole,

double throw, normally open relay 4| is connected,

to limit switch 35 through conductor |01 while a similar relay 42 is connected to limit switch 36 by conductor |06. The two limit switches 35, 36 are coupled to one ofthe leads |0| by wires |09, ||0 respectively. A conductor joins relay 4| with the other lead |0| and a corrponding conductor ||2 couples relay 42 with the same lead |0|. Relays 4|, 42 are electrically interlocked,

as shown, a conductor I|3 joining the solenoid 4|a of relay 4| with a terminal 42h of relay 42, and a conductor ||4 joining solenoid 42a with terminal 4|b of relay 4|. The two relay circuits are completed through wires ||5, ||6, which couple the relays to conductors |05, |06 respectively, and through a lead Illa which connects relay 4| to conductor Now motor 31 is energized through conductors |05, |06, which respectively energize solenoids ||1, ||8 which in turn move a double-ended pawl ||9 over ratchet |20 to permit a very small increment of lateral movement of the guide rest |9. It is clear that motor 30 is always driven in one direction or the other, depending on which relay 4|, 42 is closed, and that motor 31 is energized only momentarily, at each reversal of motor 30.

Continuing the description of Fig. 3, each of the photocells 45, 48, 49 and 50 is coupled in parallel with an ampliiier |25, |28, |29 and |30, respectively, and these amplifiers are coupled in series with leads |0| through conductors |3||30 inclusive. Variable resistances |39, |40, |4| and |42 may be in circuit with the amplifiers to adjust the balance between relays 53, 55 and 56,

which control motor 54 (which regulates the position of the cutting tool with respect to the reproductive bed). Motor 54 is connected to a lead |0| by a wire |43 and is coupled to a double pole. double throw, normally open relay 53 by conductors' |44, |45. Relay 53 has its solenoid 53a energized through conductors |46, |41 joined to conductors |36, |32, respectively. A relay 55 is coupled to conductors |34 and |32 by a conductor |48. This same relay, which controls the up motion of the cutting tool (through motor 54) is connected to relay 53 by a, wire |49 and to a lead |0| by another wire |50. Relay 56, which controls the down motion of the cutting tool, is connected to relay 53 through wire |5| and to conductors |32, .|36 by conductor |46a. Another conductor |52 connects relay 56 with a lead |0|. Thus relays 55, 56, which are normally closed, may open alternately when electric current flows through their solenoids, provided relay 53 is energized, to cause rotation of motor 54 to effect vertical movement of the carving tool. If photocells 45 and 49 are in an intensity balance, then there is an electrical balance conductor |36 and |32,

and relay 53 remains open, so that motor 54 is not energized. If, however, photocells 45 and 49 are not in an intensity balance, then conductors |36, |32 have a diil'erence in potential and a current ilows through conductors |46, |41 and the coil 53a of relay 53 to close the relay. Nowince the point of light which balanced photocell 45 to 49 must passA by photocell 50 or 46, according as the land profile is rising or declining, this will leave either relay. 56 or 56 de-energized, which will operate motor 54 in the corresponding direction.

When using nontransparent objects such as photographic prints, the unit photocells are constructed as shown in Fig. '7, with photocell |55 at the end of a light-tight casing |56 and a mirror |51, with 50% reiiectance, set at an angle of 45 relative to the longitudinal axis of casing |56. A converging lens |59 is so located as to focus rays of light reflected by mirror |51 from lamp |59 on a narrow aperture |60 at the end o! the casing. Lamp |59 may have a reilector |6| to concentrate its rays ou converging lens |62 which focuses the rays on the mirror. The light rays passing through aperture |60 are reflected by the surface of the nontransparent print I2 and pass back through the mirror to the photocell 155, which is activated accordingly. The three-cell unit for use with photographic prints will consist of three units like the one of Fig. '1.

It will be vclear that many diierent arrangements may be made to accomplish the results of the invention. If the reproductive bed is laminated with paint or other contrasting color layers fat regular intervals, the cutting tool will form ilcation, the apparatus can be made to Worky from oblique photographs. The stereos may be positives, positive transparencies, or negatives. Change from intaglio to relief type reproductions may be made by interchanging conductors |44, 145 on motor 54 and changing the position of the reproductive bed with relation to the datum plane. The carved bed may have its .surface hardened by layers of shellac or metal deposited electrolyticallinand in other ways, and may then be used as a master mold for the reproduction of like objects by stamping, pressing or casting. Many other details may be modified within the scope of the appended claims, and other uses for the apparatus will suggest themselves.

What I claim is:

1. A stereoscopic modeling machine for reproducing in three dimensions mi a reproductive bed the contour of an object photographed stereoscopically, comprising, in combination, supporting means for a pair of stereoscopic photographs; carving means for cutting into the reproductive bed; power driven means for moving the carving means across the face of the reproductive bed longitudinally; means actuated when the carving means has completed its transit across the face of the reproductive bed to cause the carving means to move through a small increment laterally or at right angles to the rst transit and then start another transit means to translate the independent small movements of the set of photocells into movements of the carving tool to cut into the reproductive bed proportionately to the independent displacements of the photocell set.

2. The invention according to claim 1, wherein the set of photocells comprises three cells in a row, and the photocell which is moved over the first stereo is exactly lined up with the photocells in the set. so that when the carving tool effects a transit from end to end of the reproductive bed. the photocells likewise move in the same straight line path over the respective stereos; the middle photocell of the setl always tending to move toward the point in the second stereo which equals in density the corresponding point in the first stereo; movement of the set in either direction being initiated by a corresponding outer photocell of the set.

3. The invention according to claim l, wherein there is an electric motor for continuously driving the carving tool and another electric motor for causing the carving tool to make the several transits across the face of the reproductive bed; a self-synchronous motor driving means to eiect said small increments of lateral movement at the end'of each transit; a pair of limit switches being in circuit with the self-synchronous motor and being Yclosed alternately at the end of each transit to energize the self-synchronous motor;

and another self-synchronous motor providing across the face of the reproductive bed in a path parallel to the iirst transit but in the opposite direction; said last named means then causing another small movement parallel to the firstnamed small increment and in the same direction; the carving tool thus moving over substantially the entire surface of the reproductivebed; a photoelectric cell circuit comprising a photocell which is moved synchronously with the carving tool adjacent to one of the stereos and a set of several photocells which is movable with the carving tool but adjacent to the second stereo; a mounting for the set of photocells permitting small movements thereof independent of any lateral or longitudinal movement of the carving tool; means responsive to the varying densities of points on. the two stereos to cause the photocell set to automatically center itself over points in the second stereo which exactly correspond in density to points in the first stereo; the circuit containing said photocells being electrically balanced when the photocell set is exactly centered as described; means for mounting the carving tool to permit movement thereof substantially at right angles to the surface of the reproductive bed; and means mechanically connecting the set of photocells with the carving tool mounting the power to translate the movement of the set of photocells, as it seeks the electrically balanced position, into proportionate or equal movements of the carving tool at right angles to the reproductive bed.

4. A stereoscopic modeling machine for reproducing in three dimensions on a reproductive bed the contour of an object photographed stereoscopically, comprising, in combination, a table; a slide rest slidably mounted -on top of the table; a tool Vsupport slidably mounted on top of the slide rest but movable at right angles to the movement of the slide rest relative to the table; a cutting tool; means supporting the cutting tool on the tool support so that it may not only partake of` the movements of the tool support in two directions parallel to the table top but may also move at right angles to the table top; power means to actuate the cutting tools, whatever its position or movement; power-actuated means to move the tool support relative to the slide rest and in opposite directions; power-actuated means to move the slide rest in small increments at the en d of each movement of the tool support in either direction; a motor having means to eiect movements of the cutting tool at right angles to the reproductive bed; light-sensitive means capable of comparing densities of points on two stereos and adapted to close electric circuits to eect movement of said motor in one direction or the other; the amount of said movement being proportional to the displacement along the axis of separation of corresponding points of the two stereos, so that the reproductive bed is carved proportionately to the differences between the stereo pair.

tool over the entire surface of .the reproductive bed; mounting means for the cutting tool permitting movements of the cutting tool substantially at rightangles to the surface of thel reproductive bed; power means to drive -the cutting tool, whatever its position: light-sensitive means coupled in a circuit, said circuit including means to move the cutting tool at right angles to the surface of the reproductive bed and independently oi all other means; means to move the light-sensitive means; said light-sensitive means automatically comparing light values of two points on two stereos and automatically moving toward the position wherein the coupled circuit is balanced; and means connecting said light-sensitive means with the cutting tool mounting means so that movements of the light-sensitive means effect the aforesaid independent movements of the cutting tool.

6. A completely automatic machine for carving a reproductive bed in three dimensions to,

reproduce, on any desired scale, the contour of a stereoscopically photographed object, comprising, in combination, a cutting tool adapted to travel across the entire surface of reproductive bed; power means to drive the cutting tool and other power means to effect the travel thereof; lightsensitive analyzing means adapted to travel across the surfaces of a pair of stereoscopic photographs and to compare light densities of corresponding points of said pair; said analyzing means having movements independent of all other movements of the apparatus; circuits and also a motor controlled by the circuits to move the analyzing means to such a position that an electrical balance .is eiected in said circuits at the moment when points of exactly equal density in the stereo pair are exposed to the analyzing means; the electrical balanced condition effecting stoppage of the independent movements of the analyzing means; and means electrically and mechanically connecting the analyzing means with the cutting tool to effect in and out movement thereof relative to the reproductive bed, whereby the differences in elevation as recorded on the stereo pair are faithfully reproduced, on the aforesaid scale, during carving of the reproductive bed.

"1. In combination with a pair of stereoscopic images of an object to be reproduced by carving a reproductive bed in relief or in intaglio, a scanning device comprising power-driven means and a plurality of photocells moved by the powerdriven means over the images; circuits controlled by the photocells; said photocells being separated so that one photocell is moved over one image and the remaining photocells, comprising a set, are simultaneously moved over the other image of the stereo pair; the photocell set comprising three juxtaposed photocells being constructed and arranged so that they will respond individually to the light density of three adjacent points in one straight line on the image; means for mounting the photocell set so that it may move independently of all other parts of the apparatus; power means controlled by the photocells to move the photocell set; the middle photocell of the set tending always to seek the point in the second image of the stereo pair which exactly equals in density a point on the first image; the two outer photocells, when excited by an unbalanced condition due to variations in density of the points picked up, closing said circuits to cause the middle photocell to seek the light-equilibrium position; a power-driven cutting tool; and means mechanically connecting the set of photocells with the cutting tool to cause the latter to move in and out of the reproductive bed equal to or proportionately to the amount of movement of the photocell set ln reaching the light-equilibrium position. Y

LOUIS A. SCHOLZ. 

